Structural Design And Key Fabrication Process Of GaN Vertical MPS Diodes

With the continuous development of the concept of the digital era and related emerging technologies,electrical energy has gradually become the most indispensable energy in today’s society,which has put forward high requirements for the actual supply of electrical energy.Under the background of global energy shortage today,how to realize the efficient use of electrical energy has become a problem that people must face.Electronic devices are the core components of electric energy transmission and utilization,but the traditional silicon-based electronic devices have gradually approached their theoretical limits with the development of science and technology,and it is difficult to achieve further breakthrough development.Therefore,the wide bandgap semiconductor material represented by GaN,with its wide band gap,high critical electric field,high electron mobility,high thermal conductivity and other material advantages,has become a strong choice to lead the development of power electronics technology in the new era.The development trend of GaN power devices is miniaturization and high efficiency,which puts stringent requirements on device size and performance.Vertical structure is an ideal device structure to meet this development trend,which can improve device performance by increasing the three-dimensional thickness of the device.As the most commonly used rectifier element in circuit systems,Schottky barrier diodes are still facing the problem of poor breakdown characteristics,which limits their application in high-voltage and high-power systems.In order to solve this problem,this thesis takes the GaN merged PN-Schottky(MPS)diode as the entry point and conducts research on the regulation of the internal electric field of the device.The simulation of the device structure and the exploration of selective doping key process are carried out:1.A systematic simulation study on the influence of the structural parameters on the forward and reverse electrical properties of GaN MPS diodes is carried out,with the aim of forming an effective electric field shielding protection to Schottky contact and avoiding the lowering of Schottky barrier caused by high electric field.At the same time,a resistance analysis model is established to analyze the forward conduction electrical parameters of the device,and the high power characteristics of GaN MPS diodes are comprehensively considered by extracting the Baliga figure of merit(BFoM).2.To experimentally explore the selective doping of the GaN MPS diodes,a trench regrowth method was used to obtain high-quality lateral pn junction.The epitaxial structure of the device was grown by MOCVD,and based on this,the selective doping process flow of the device was proposed and summarized.Subsequent related experiments and discussions were carried out on the key process(TMAH wet treatment to repair ICP dry-etching damage,trenchselective regrowth and flattening of the regrowth interface),which will lay the foundation for further the device fabrication.3.In order to avoid the premature breakdown of the device caused by locally crowding high electric field in the corner of the p-GaN grids in GaN MPS diodes,methods of inserting T-shaped shielding rings and sidewall isolation layer are proposed to improve the breakdown voltage of the device.These two device structures obtain boosted breakdown voltage by realizing the principle of increased size of depletion region and the increased voltage supported by the insulation isolation layer,respectively.The basic structural parameters and electrical forward and reverse characteristics of the two device structures are simulated and analyzed,and the effect of reverse electric field modulation and forward conduction current spreading are discussed.